The present disclosure relates to methods of forming a semiconductor structure, and particularly to methods of forming a vacancy of a semiconductor fin within an array of semiconductor fins.
Fin field effect transistors (finFETs) employ semiconductor fins, which introduce on-wafer topography. The semiconductor fins are often formed as an array of semiconductor fins having a periodicity in order to minimize etch bias due to pattern factor, i.e., the fraction of the area of the semiconductor fins within a unit area. In this case, some of the semiconductor fins need to be removed after formation of the array of semiconductor fins in order to provide isolated semiconductor fins or a cluster of semiconductor fins spaced from other clusters of semiconductor fins.
In order to remove a single semiconductor fin while protecting adjacent semiconductor fins, a lithographically patterned mask needs to physically expose the single semiconductor fin while covering the adjacent semiconductor fins. Thus, two sidewalls of a patterned photoresist need to be positioned within the spaces between the single semiconductor fin and the two adjacent semiconductor fins in order to ensure that only a single semiconductor fin is removed without removing any additional semiconductor fins. However, as the pitch of the semiconductor fins decreases, it becomes difficult to remove a single semiconductor fin while protecting adjacent semiconductor fins because of overlay tolerances of lithographic processes. As of 2012, single fin cut for a fin pitch less than 40 nm is very challenging. Thus, a method is desired for ensuring that only a single semiconductor fin can be removed from an array of semiconductor fins while reliably protecting adjacent semiconductor fins.